Method of Manufacturing Porous Bearing Component, and Method of Manufacturing Fluid Dynamic-Pressure Bearing Furnished with the Porous Bearing Component

ABSTRACT

Manufacturing method for impregnating with lubricant a porous bearing material retained in a bearing retaining cavity in a bearing retainer. Under a reduced-pressure space within a vacuum chamber, a bearing structural unit in which a porous bearing material is retained in a bearing retaining cavity in a bearing retainer is, with an opening in the bearing structural unit directed down, immersed in or contacted on lubricant to cover over the bearing-structural-unit opening; by then restoring chamber pressure, the porous bearing material is impregnated with the lubricant. The manufacturing method controls to a minimum adhesion of lubricant to the bearing-retainer exterior, to eliminate as far as possible the trouble of lubricant cleanup, and at the same time makes the impregnation of the porous bearing material with lubricant more sound and facilitates the impregnation job despite its being under a reduced-pressure atmosphere.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to methods of manufacturing fluiddynamic-pressure bearings furnished with a lubricant-impregnated porousbearing component; in particular, the present invention relates tomethods of manufacturing fluid dynamic-pressure bearings that areinstalled in spindle motors for driving hard disks and likeinformation-recording devices.

2. Description of the Related Art

Conventionally, in order to impregnate a porous substance with alubricant, a method referred to as vacuum impregnation has beenemployed.

For example, Japanese Patent No. 3,010,718 discloses a method ofimpregnating a porous object with lubricating fluid by evacuating acontainment space containing the lubricating fluid, with the porousobject being immersed in the fluid. It is possible to apply this methodto a porous bearing component of a form in which the porous bearingmaterial is retained in the interior of a bearing housing. One drawbackwith this method, however, is that because the bearing housing isimmersed in the lubricating fluid, the fluid sticks to the outersurfaces of the bearing housing, making it necessary to wipe thelubricating fluid off the outer surfaces of the bearing housing afterimpregnating the porous bearing material with the lubricating fluid,which is a laborious task.

Furthermore, if the bearing housing is in the form of a close-endedcylinder, the porous bearing material can be impregnated withlubricating fluid by putting the bearing housing open-end up, seatingthe porous bearing material within the housing and then, withlubricating fluid filling the bearing housing, in that state evacuatingthe environment surrounding the bearing housing. In this case, however,due to the bursting of air bubbles discharged from the voids in theporous bearing material, there is a likelihood of the lubricating fluidsplattering and contaminating the outer periphery of the bearinghousing, leading to difficulties similar to those described above. Thisalso runs the risk, moreover, that the porous bearing material will notbe sufficiently impregnated with the lubricating fluid.

Another example is the vacuum-assisted resin impregnation technique—amethod for impregnating a porous component with a syntheticresin—described in Japanese Unexamined Pat. App. Pub. No. H11-033389, inwhich a container holding synthetic resin is placed within vacuumatmosphere (a vacuum furnace), air within the vacuum atmosphere isremoved, and then, under the vacuum atmosphere, a porous component isimmersed in the synthetic resin within the container to impregnate theporous body with the synthetic resin. Although it is possible to usethis technique to impregnate with lubricating fluid a porous bearingmaterial retained in a bearing housing, the technique gives rise to thetrouble of having to wipe off lubricating fluid adhering to the outsideof the bearing housing, likewise as with the method described above.Moreover, the published application makes no mention of the specific wayin which, within the vacuum furnace, the porous component from which airhas been removed is introduced into the lubricant while the vacuumatmosphere is maintained. Although component introduction would bepossible employing an actuator whose manipulation inside the vacuumfurnace is possible from without, such equipment is generally expensiveand would make for a heavy equipment-cost burden in a mass productionsituation.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is in providing a method ofmanufacturing a fluid dynamic-pressure bearing furnished with a porousbearing component, to enable reliable lubricant impregnation of a porousbearing material contained in a bearing retainer.

Another object of the present invention is to provide a method ofmanufacturing a fluid dynamic-pressure bearing including a porousbearing component, whereby the impregnation work can be easily carriedout despite its being done under a reduced-pressure atmosphere.

Still another object of the present invention is to provide a method ofmanufacturing a fluid dynamic-pressure bearing including a porousbearing component, whereby labor of cleaning up lubricant can beeliminated to the extent possible by minimizing lubricant adhering tothe exterior of the bearing retainer when impregnating with lubricant aporous bearing material housed in a bearing retainer.

According to a method of manufacturing a lubricant-impregnated porousbearing component, and to a method of manufacturing a fluiddynamic-pressure bearing of the present invention to attain theabove-described objects, a bearing structural unit is disposed in avacuum chamber in which lubricant is contained, and one end portion ofthe bearing retainer is immersed in or contacted on the lubricant, withthe one end of the bearing retaining cavity turned down, under a statein which the pressure in the vacuum chamber is reduced, and thelubricant is infiltrated into the inside of the bearing retainer while astate in which the one end of the bearing retaining cavity is occludedby the lubricant is maintained.

Thus, by putting a bearing structural unit retaining the porous bearingmaterial in the bearing retaining cavity of the bearing retainer under areduced-pressure atmosphere, as compared to the case in which thelubricant infiltrates the inside of the bearing retaining cavityincluding the voids in the porous bearing material, air is removed andair pressure is reduced more easily and more certainly. By immersing inor contacting on the lubricant one end portion of the bearing structuralunit in the lubricant arranged in a reduced air pressure space with theone end portion turned lower (namely, within a scope of the presentinvention, in the same direction as the gravitational direction, or in adirection inclined with respect to the gravitational direction),occluding the one end portion with the lubricant, it is possible toclose off the inside of the bearing retaining cavity from the outside.Herein, a bearing structural unit in which the inside of the bearingretaining cavity has air tightness against the outside except for theone end portion is used as it is, whereas a bearing structural unitwithout such air tightness is used with the inside of the bearingretaining cavity except for the one end portion placed underairtightness.

After that, when the pressure is restored while maintaining thelubricant-occluding state at the one end portion of the bearingretainer, the reduced pressure state of the inside of the bearingretaining cavity is maintained against the outside, and this makes thelubricant to move upward in the bearing retaining cavity. Thereby, byinfiltrating the lubricant in the porous bearing material into thebearing retaining cavity, a porous bearing component impregnated withthe lubricant can be acquired. Since the inside of the bearing retainingcavity including the gap of the porous bearing material is evacuated ofair and the pressure is reduced, the splattering of lubricant due to thebursting of air bubbles is prevented.

Since one end portion of the bearing structural unit is immersed in orcontacts on the lubricant except for the inside of the bearing retainingcavity, and the outside of the bearing retainer does not contact thelubricant except for the one end portion thereof, and thus the lubricantis prevented from getting splattered due to the bursting of air bubbles,the time and trouble of cleanup work involving the wiping off oflubricant adhering to the exterior of the bearing retainer is curtailed.

In addition, the porous bearing material retained in the bearingretaining cavity is immersed in or contacted on the lubricant with theone end of the bearing retaining cavity occluded by the lubricant byimmersing the one end of the bearing structural unit in, or contactingit on, the lubricant arranged in the reduced-pressure space, with theone end portion turned down. In this case, once the porous bearingmaterial retained in the bearing retaining cavity is immersed in ormakes contact with the lubricant, the lubricant permeates the voids inthe porous bearing material by the agency of surface tension, enablingthe more certain impregnation of the porous bearing material with thelubricant.

Further, the one end of the bearing retainer is occluded by thelubricant by immersing in or contacting on the lubricant the one end ofthe bearing structural unit to immerse in or contact on the lubricantthe porous bearing material retained in the bearing retaining cavity,and then, after a predetermined time has passed, the pressure in thevacuum chamber is restored while maintaining the one end portion of thebearing retainer in the state in which it is occluded by the lubricant.Thereby, it is possible to more certainly impregnate the porous bearingmaterial with the lubricant. In this case, the predetermined time may beabout five minutes, for example; however, it is preferable that thepredetermined time is changed in accordance with the kind of thelubricant used and the structure of the bearing.

Thus, since the manufacturing method of the present invention can bepracticed by performing the operation for changing the relative verticalpositional relation between the bearing structural unit and the surfaceof the lubricant in a reduced-pressure space, even in thereduced-pressure space, the operation is easily carried out and therequired material and equipment costs can be effectively reduced. Inaddition, because the outside of the bearing retainer does not contactthe lubricant except for the one end portion thereof and the lubricantis prevented from getting splattered due to bursting of air bubbles, thetime and trouble of cleanup involving the wiping off of lubricantadhering to the outside of the bearing retainer is curtailed. Further,in cases in which the open end of the bearing housing is directedupward, the lubricating fluid is pooled within the bearing housing, andthe bearing housing is evacuated, it is necessary to measure thelubricating fluid and inject it into the bearing housing; however,according to the present invention, it is not necessary to measure thelubricating fluid, curtailing costs by that which would otherwise beexpended to do so.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the attached drawings that form a part of this originaldisclosure:

FIG. 1A is a sectional view of a bearing structural unit, wherein thesituation under reduced pressure in the process of manufacturing aporous bearing component is represented;

FIG. 1B is a sectional view of the bearing structural unit, wherein astate, in the process of manufacturing the porous bearing component, inwhich part of the bearing structural unit is immersed in a lubricant isrepresented;

FIG. 1C is a sectional view of the bearing structural unit, wherein thesituation when pressure is restored in the process of manufacturing aporous bearing component is represented;

FIG. 2A is a sectional view representing, in a pressure-reductionsituation, a manufacturing apparatus for manufacturing the porousbearing component;

FIG. 2B is a sectional view representing, in an immersion situation, amanufacturing apparatus for manufacturing the porous bearing component;

FIG. 3 is a sectional view of a fluid dynamic-pressure bearing furnishedwith the porous bearing component;

FIG. 4 is a plan view of the bearing structural unit; and

FIG. 5 is a sectional view of a spindle motor in which the fluiddynamic-pressure bearing is utilized.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

(1) Fluid Dynamic-Pressure Bearing Structure

FIG. 3 is a sectional view of a fluid dynamic-pressure bearing that is amanufacturing target. This fluid dynamic-pressure bearing is made up ofa rotor 10 that is a shaft-end structural component of the motor, and abearing structural unit 12. As the bearing structural unit 12, a porousbearing component impregnated with lubricant, manufactured through thesteps shown in FIGS. 1A to 1C is utilized. In the present embodiment,the rotor constitutes the shaft-end structural component but theconfiguration is not thereby limited; the shaft-end structural componentmay be provided on the stator end of the motor, or may be provided onthe rotary or stationary end of the embodying device apart from themotor. Further with regard to alternative embodiments, although a fluiddynamic-pressure bearing furnished with a porous bearing componentmanufactured according to the present invention is particularly suitedto utilization in spindle motors for driving information recordingdevices such as hard disks, the bearing is utilizable in rotatingmachines apart from spindle motors.

The rotor 10 is constituted by a cuplike rotor hub 10 a, and a shaft 10b that is anchored in a snug fit into the rotational center of the rotorhub 10 a. On the inner circumferential surface of the outercircumferential wall of the rotor hub 10 a, a rotor magnet 14 isattached by adhesive or like means.

The bearing structural unit 12 has a housing 16 (a bearing retainer) inthe form of a close-ended cylinder, and a bearing sleeve 18 (a porousbearing material) in the form of a hollow tube coaxially mounted withinthe housing 16. A journaling bore 18 b axially through which the shaft10 b penetrates is formed through the central portion of the bearingsleeve 18.

Sheet metal consisting of a material such as stainless steel or acopper-based or aluminum-based alloy is press-worked to form the housing16 in the shape of an approximate cup whose bottom side is closed off.Nevertheless, the method of manufacturing the bearing retainer is notthereby limited.

The bearing sleeve 18 is constituted from a porous sintered body,rendering the inner-circumferential-surface portion of the journalingbore 18 b of the bearing sleeve 18 a porous surface. The substance ofthe bearing sleeve 18 is not particularly limited; molded and sinteredsubstances in which powders of various metals, powders of metalcompounds, or a nonmetal powders are the source material may beemployed. Examples of such source materials include Fe—Cu, Cu—Sn,Cu—Sn—Pb, and Fe—C. The interior of the bearing sleeve 18 of poroussintered manufacture is impregnated with the same oil 15 that isretained in a later-described bearing gap.

The shaft 10 b is inserted through the journaling bore 18 b in thebearing sleeve 18. The outer circumferential surface of the shaft 10 bradially opposes, across an interspace, the inner circumferentialsurface of the bearing sleeve 18, and the leading-end face of the shaft10 b axially opposes, across an interspace, the inner surface of theclosed-off end part 16 a (closed-off end surface) in the bottom portionof the housing 16. The bearing sleeve 18 is mounted so that itsdepth-wise endface (in FIGS. 1A to 1C, the endface on the upper side; inFIG. 3 and FIG. 5, the endface on the lower side) axially opposes,across an interspace, closed-off end part 16 a of the housing 16. Theendfaces along the openings in the housing 16 and the bearing sleeve 18axially oppose, across an interspace, a shaft-end ringlike planarsurface 10 a 1 extending radially outward from the outer circumferentialsurface of the shaft 10 b along where the shaft protrudes from the rotorhub 10 a.

The interspace formed between the endfaces along the openings in thehousing 16 and the bearing sleeve 18, and the surface of the rotor hub10 a along where the shaft protrudes, the interspace formed between theinner circumferential surface of the bearing sleeve 18 and the outercircumferential surface of the shaft 10 b, the gap formed between theinner surface of the closed-off end part 16 a of the housing 16, and thelower endface of the shaft 10 b, and the adjoining gap formed betweenthe depth-wise endface of the bearing sleeve 18 and the inner surface ofthe closed-off end part 16 a of the housing 16 (hereinafter, each ofthese gaps—as well as the gap formed in a later-described communicatingpassage 19—will together be denoted “the bearing gap”) are allcontinuous. The oil 15 is continuously retained in these continuous gapswithout interruption, constituting a bearing of a full-fill structure.

An axially directed groove 18 a reaching from the endface on the upperside to the endface on the lower side of the bearing sleeve 18 isprovided on the sleeve outer circumferential surface (cf. FIGS. 1, 3 and4). The axially directed groove 18 a is formed to have a semicircularcross-sectional conformation by a pressing, milling or similar processon the sleeve. The cross-sectional shape of the axially directed groove18 a is not limited to being semicircular, and can have othergeometries, such as an approximate rectangular form for example.Attaching the thus-structured bearing sleeve 18 to the innercircumferential surface of the housing 16 forms the communicatingpassage 19 from the axially directed groove 18 a and the innercircumferential surface of the housing 16, and the oil 15 is retainedalso within the communicating passage 19. Both axial end portions of thegap formed between the inner circumferential surface of the bearingsleeve 18 and the outer circumferential surface of the shaft 10 bcommunicate through the communicating passage 19, via the gap formedbetween the endfaces along the openings in the housing 16 and thebearing sleeve 18, and the surface of the rotor hub 10 a along where theshaft protrudes, as well as the gap formed between the depth-wiseendface of the bearing sleeve 18 and the inner surface of the closed-offend part 16 a of the housing 16.

An annular flange portion 16 b is provided at the circumferentially openend part of the housing 16. The flange portion 16 b is formed in asloped-surface contour so as to project radially outward and so that theouter peripheral surface constricts as it separates from the open end.An annular wall part 10 c is provided on the rotor hub 10 a, standingout, in the same direction as the shaft 10 b, shorter than the outercircumferential wall of the rotor hub 10 a, from the shaft-end ringlikeplanar surface 10 a 1 along its outer periphery. An annular recess, thefloor of which is the shaft-end ringlike planar surface 10 a 1, isformed between the annular wall part 10 c and the shaft 10 b. The innercircumferential surface of the annular wall part 10 c and the outerperipheral surface of the flange portion 16 b radially oppose each otherin a non-contacting state.

By the outer peripheral surface of the flange portion 16 b being formedin a sloped-surface contour, the radial gap measurement in theinterspace between the inner circumferential surface of the annular wallpart 10 c (that is, the surface of a cylindrical surrounding wall), andthe outer peripheral surface of the flange portion 16 b, graduallyincreases heading toward a bracket 30, represented in FIG. 5, (that is,in the direction of the leading-end portion of the annular wall part 10c). In other words, the inner circumferential surface of the annularwall part 10 c and the outer peripheral surface of the flange portion 16b associatively constitute a taper seal section 28. With regard to theoil 15 retained within the gaps described above, in the taper sealsection 28 the surface tension of the oil 15 and the external airpressure balance, forming the boundary surface between the oil 15 andair into a meniscus.

The taper seal section 28 functions as an oil reservoir, and thelocation of the oil boundary surface shifts appropriately in accordancewith the volume of the oil retained in the taper seal section 28.Accordingly, the oil 15 retained in the taper seal section 28 issupplied into a bearing section, to be explained later, in accordancewith any amount by which the retained oil decreases; meanwhile anyamount by which the volume of the oil 15 increases due to thermalexpansion another cause is accommodated within the taper seal section28.

Thus, forming a tapered interspace between the outer peripheral surfaceof the flange portion 16 b of the housing 16, and the innercircumferential surface of the annular wall part 10 c of the rotor hub10 a, to constitute the surface-tension-exploiting taper seal section 28enables the taper seal section 28 to be diametrically larger, and theaxial dimension of the taper seal section 28 to be relatively large.Accordingly, the capacity within the taper seal section 28 is increased,and the taper seal section 28 can sufficiently follow the thermalexpansion of the generous quantity of oil 15 retained in a full-fillstructured dynamic pressure bearing.

In order to induce fluid dynamic pressure in the oil 15 upon rotation ofthe rotor 10, herringbone grooves 20 a made up of linked pairs of spiralstriations inclined in orientations running counter to the rotationaldirection are formed on the inner circumferential surface of the bearingsleeve 18 along its open end, wherein a radial bearing section 20 alongthe opening in the sleeve 18 is constituted by the herringbone grooves20 a and the outer circumferential surface of the shaft 10 b. The axialdimension of the spiral-striation portions of the herringbone grooves 20a located toward the sleeve open end is determined so as to be greaterthan that of the spiral-striation portions located depth-wise, whereinthe herringbone grooves 20 a are formed so that, in response to rotationof the rotor 10, maximum dynamic pressure is generated in a regionbiased depth-wise from the center, and at the same time, pressurepushing the oil 15 depth-wise is produced. Due to this depth-wisepressing force, the internal pressure of the oil 15 retained in the gaplocated deeper than the radial bearing section 20 along the open end iskept at atmospheric pressure (external air pressure) or greater.

Likewise, in order to induce fluid dynamic pressure in the oil 15 uponrotation of the rotor 10, herringbone grooves 22 a made up of linkedpairs of spiral striations inclined in orientations running counter tothe rotational direction are formed on the inner circumferential surfaceof the bearing sleeve 18 along its bottom end, wherein a radial bearingsection 22 along the depth-wise end of the sleeve 18 is constituted bythe herringbone grooves 22 a and the outer circumferential surface ofthe shaft 10 b. The two sets of spiral striations forming theherringbone grooves 22 a in the depth-wise radial bearing section 22 areconfigured so that groove fundamentals, such as axial dimension andangle of inclination with respect to the rotational direction, or groovewidth and depth, are the same in order that the two sets of spiralstriations generate substantially equal pumping force. In other words,two sets of spiral striations are configured to have line symmetry withrespect to where they link (a circumference of the bearing sleeve 18 ata given axial position). Accordingly, in the depth-wise radial bearingsection 22, the dynamic pressure maximum appears midway of the bearingaxially.

Further, pump-in spiral grooves 24 a—as represented in FIG. 4—thatinduce in the oil 15 radially inward-heading (toward the shaft 10 b)pressure when the rotor 10 spins are formed in the endface (bearing-endringlike planar face) along the open end of the housing 16, and betweenthe pump-in grooves 24 a and the shaft-end ringlike planar surface 10 a1 of the rotor hub 10 a, a thrust bearing portion 24, as indicated inFIG. 3, is constituted.

The herringbone grooves 20 a and 22 a provided in the opening-wardradial bearing portion 20, and the depth-wise radial bearing portion 22can be formed by a pressing operation on a bearing sleeve 18 made of asintered material. In addition, the spiral grooves 24 a with which thethrust bearing portion 24 is provided can be formed at the same time thehousing 16 is press-molded.

It will be appreciated that the endface along the free end of the shaft10 b, and the inner surface of the closed-off end part 16 a of thehousing 16 function as a static pressure bearing section that exploitsinternal pressure of the oil 15 having been heightened by the spiralgrooves 24 a of the thrust bearing section 24.

A fluid dynamic bearing manufactured in this way can be utilized, forexample, in a spindle motor as represented in FIG. 5. Specifically, thehousing 16 is anchored into a round boss portion 30 a provided in thebracket 30, and a stator 27 is secured to the outer circumferentialsurface of the boss portion 30 a so as to radially oppose the rotormagnet 14. An annular retaining ring 25 is fastened by an adhesive orsimilar means to the leading end of the annular wall part 10 c beyondthe taper seal section 28. The annular retaining ring 25 is fittogether, in a non-contacting state, with the underside of the flangeportion 16 b (FIG. 5) to prevent the rotor 10 (shaft-end structuralcomponent) from falling out of the housing 16 of the bearing structuralunit 12. Fitting information-recording discoid plate(s) externally over,and retaining the plate(s) on, the rotor hub 10 a enables the spindlemotor to be utilized as a disk drive.

(2) Manufacture of a Lubricant-Impregnated Porous Bearing Component

Porous bearing components impregnated with lubricant are manufacturedutilizing the manufacturing apparatus represented in FIG. 2A and FIG.2B.

The manufacturing apparatus is furnished with: an oil bath 52, inside avacuum constant-temperature vat 50, in which the oil 15 (lubricant) isstored; a support frame 56 that is vertically driven by air-pressureactuated linear guides 54; and a pallet 58, detachably supported on thesupport frame 56, that moves vertically within the oil bath 52. Thepallet 58 is provided with a grip 64 on a carrying plate 62 evenlyperforated by numerous small through-holes 60. It will be appreciatedthat the means for vertically driving the pallet 58 and associatedcomponents can be selected as appropriate to a given implementation.

In manufacturing a porous bearing component, as indicated in FIG. 1A andFIG. 2A, in the vacuum constant-temperature vat 50, a predeterminedamount of oil 15 is pooled in the oil bath 52. Then bearing structuralunits 12, in which the bearing sleeves 18 are attached coaxially intothe housings 16, are placed with their open ends turned down on thecarrying plate 62 on the pallet 58, and the pallet 58 is loaded onto thesupport frame 56 having been positioned above the oil 15 in the oil bath52. In this state, the pressure inside the vacuum constant-temperaturevat 50 is reduced to a predetermined vacuum level (for example, 0.1 torror less, but the vacuum is not limited to being that level) with avacuum pump or like device. Further, in order to reduce the viscosity ofthe oil 15, the temperature within the vacuum constant-temperature vat50 is kept at 70° C. Herein, although it is the case that the more thetemperature is raised, the more the viscosity is lowered, maintaining atemperature in excess of 90° C. can lead to troubles with themanufacturing work. By the same token, a temperature less than 60° C. isundesirable because the viscosity of the oil 15 does not lowersufficiently.

Then, the inside of the vacuum constant-temperature vat 50 is left underthis reduced-pressure state for a predetermined time (for example, 40minutes, but the duration is not limited to that), to reduce thepressure in, and reliably evacuate the air from, the inside of thehousing 16 (the inside of the bearing retaining cavity), including thevoids in the bearing sleeve 18, bringing the bearing structural unit 12down to a requisite vacuum level. It will be appreciated that in orderto lower the viscosity of the oil 15, the temperature of the oil 15within the oil bath 52 may be maintained at above-noted necessarytemperature.

After that, the linear guides 54, are driven to lower the support frame56 and immerse, as illustrated in FIG. 1B, in the oil 15 the carryingplate 62 on the pallet 58, and the open-end portions, being the bottomends, of the bearing structural units 12 (including the open ends of thebearing sleeves 18) set on the carrying plate 62, occluding the bottomends of the bearing structural units 12, as indicated in FIG. 2B. Thehousing 16 interior is in this way put into an occluded state, and thatstate is left as it is for five minutes. In that interval, the oil 15permeates the voids in the bearing sleeve 18 by the agency of surfacetension. During this immersion period, the height of the pallet 58 orthe position of the oil 15 surface is adjusted so that the open ends ofthe bearing structural units 12 constantly remain immersed in the oil15. For example, occluding the open ends of the bearing structural units12 with oil 15 can be realized by making the pallet 58 stationary andelevating the oil bath 52, or by increasing the amount of oil 15 toelevate the oil surface.

When the pressure inside the vacuum constant-temperature vat 50 issubsequently restored (normally it is restored to atmospheric pressure),because a reduced pressure state in the inside of the housing 16including the inside of the journaling bore 18 b is sustained, as shownin FIG. 1C, the oil 15 infiltrates the housing 16 interior including thejournaling bore 18 b interior, sufficiently impregnating the bearingsleeve 18 with the oil 15. In this case, it is preferable that thereduction and restoration of pressure are carried out so that the oil 15rises to the upper end of the journaling bore 18 b. Holding the insideof the vacuum constant-temperature vat 50 in this state for a requisitetime (several minutes for example), enables the action of impregnatingthe bearing sleeve 18 with the oil 15 to be made the more certain. Gasintroduced in restoring the pressure within the vacuumconstant-temperature vat 50 may be an inert gas, such as helium ornitrogen, whose solubility with respect to the oil 15 is low.

It should be understood that means can be adopted in order to make it sothat before the oil 15 has sufficiently infiltrated the housing 16, theocclusion of the open end of the bearing structural unit 12 by the oil15 does not break due to the liquid surface of the oil bath 52 droppingwhen the oil 15 infiltrates the housing 16 interior. Such means include:(i) having the position of the pallet 58 with respect to the oil bath 52when the lower end portion of the bearing structural unit 12 is immersedin the oil 15 be fixed and, taking into consideration the drop in theliquid surface of the oil bath 52, setting the depth to which the lowerend portion of the bearing structural unit 12 is immersed in the oil 15so that the occlusion is not broken; (ii) in response to a drop in theliquid surface of the oil bath 52, lowering the position of the pallet58 with respect to the oil bath 52; and (iii) monitoring the height ofthe surface of the oil 15 with a sensor, and if the level drops below aprescribed height, automatically injecting oil into the bath 52.

Thereafter, by driving the linear guides 54 to elevate the support frame56 (alternatively, by lowering the oil bath 52, or externallydischarging the oil 15 in the oil bath 52 to reduce the oil volume) theocclusion of the open end of the bearing structural unit 12 by the oil15 is broken, whereby excess oil in the journaling bore 18 b interiorand other regions drains, yielding a lubricant-impregnated porousbearing component in which the bearing sleeve 18 is impregnated with theoil 15.

In this way carrying out the operation of varying the relative verticalpositional relationship between the pallet 58 within the vacuumconstant-temperature vat 50, and the level of the oil in the oil bath 52enables the manufacture of lubricant-impregnated porous bearingcomponents to be performed, thanks to which operations in the vacuumconstant-temperature vat 50 are facilitated, and material costs for thenecessary machinery and facilities are effectively minimized.Furthermore, since the inside of the housing 16, including the voids inthe bearing sleeve 18, is evacuated and reduced in pressure beforehand,bursting of air bubbles that splatters the oil 15 is prevented. Inaddition, except for the housing 16 interior, the bearing structuralunit 12 is immersed single-ended in the oil 15; thus, due to the factthe exterior of the housing 16 except for the one end portion does notcome into contact with the oil 15, and to the fact that splattering ofthe oil 15 due to air bubbles bursting is prevented, the labor of wipingaway lubricant adhering to the exterior of the housing 16 and ofassociated cleanup is curtailed.

For bearing structural unit implementations in which the depth-wise endof the housing is open, a lubricant-impregnated porous bearing componentcan be obtained by using a jig or similar tool to temporally close offthe depth-wise end of the housing and render it airtight against theexterior, and processing the unit likewise as above. The jig or similartool employed in this case may be detached following completion of theoil-impregnation job.

The present invention is not limited to the above-described embodimentsand various changes or modifications are possible without deviating fromthe scope of the present invention.

Specifically, the present invention is not limited to the dynamicpressure bearing, motor, or the recording disk drive illustrated in theforegoing embodiment. Further, the presence/absence ofdynamic-pressure-generating grooves in, the components forming, or thegeometry of, the bearing sections of the dynamic pressure bearing arenot limited to those of the foregoing embodiment.

Furthermore, with the embodiment illustrated in the figures, adescription was made giving the example of a so-called shaft-rotatingspindle motor in which the shaft 10 b is fixed to the rotor hub 10 a toconstitute the rotor 10; however, the present invention is alsoapplicable to so-called shaft-stationary spindle motors in which theshaft constitutes a portion of the stationary component.

1. A method of manufacturing a lubricant-impregnated porous bearingcomponent, in which a bearing retainer having a bearing retaining cavityat least one end of which is open, and a tubular porous bearing materialretained in the bearing retaining cavity in the bearing retainerconstitute a bearing structural unit in which thebearing-retaining-cavity interior except for the one end portion of thebearing retainer has airtightness against the outside, the methodimpregnating the porous bearing material with a lubricant, andcomprising: a step of, within a vacuum chamber in which the lubricant iscontained, disposing the bearing structural unit separated from thelubricant; a step of reducing the pressure within the vacuum chamber inwhich the bearing structural unit is disposed; a step, under thereduced-pressure state within the vacuum chamber, and with the one endof the bearing retaining cavity directed down, of immersing in, orcontacting on, the lubricant the one end portion of the bearing retainerto occlude the one end of the bearing retaining cavity; a step ofmaintaining the one end of the bearing retaining cavity occluded by thelubricant and infiltrating the lubricant inside the bearing retainer;and a step of, with the one end of the bearing retaining cavity occludedby the lubricant, restoring the pressure within the vacuum chamber.
 2. Alubricant-impregnated porous bearing component manufacturing methodaccording to claim 1, wherein in immersing the one end portion of thebearing structural unit in, or contacting the one end portion on, thelubricant arranged within the vacuum chamber, to put the one end of thebearing retaining cavity in an occluded state, the porous bearingmaterial retained within the bearing retaining cavity is immersed in orcontacted on the lubricant.
 3. A lubricant-impregnated porous bearingcomponent manufacturing method according to claim 2, wherein afterimmersing the one end portion of the bearing structural unit in, orcontacting the one end portion on, the lubricant arranged within thevacuum chamber, and immersing in or contacting on the lubricant theporous bearing material retained within the bearing retaining cavity, toput the one end of the bearing retainer in an occluded state, followingthe elapse of a predetermined period of time, pressure is restored whilethe state in which the one end portion is occluded by the lubricant ismaintained.
 4. A lubricant-impregnated porous bearing componentmanufacturing method according to claim 1, further comprising anoperation, in maintaining the one end of the bearing retaining cavityoccluded by the lubricant and infiltrating the lubricant inside thebearing retainer, of elevating the liquid surface of the lubricantwithin the vacuum chamber, or lowering the bearing retainer.
 5. Alubricant-impregnated porous bearing component manufacturing methodaccording to claim 1, wherein: the bearing structural unit is of astructure in which the bearing-retaining-cavity interior except for theone end portion of the bearing retainer does not have airtightnessagainst the outside; and the manufacturing method further comprises thestep of, before the one end portion of the bearing structural unitdisposed within the vacuum chamber is immersed in or contacted thelubricant, making the bearing retainer except for the one end of thebearing retaining cavity airtight against the outside.
 6. Alubricant-impregnated porous bearing component manufacturing methodaccording to claim 1, wherein subsequent to the step of restoring thepressure within the vacuum chamber with the one end of the bearingretaining cavity being occluded by the lubricant, the occlusion by thelubricant is broken after the elapse of a predetermined period of time.7. A lubricant-impregnated porous bearing component manufacturing methodaccording to claim 1, wherein the porous bearing material constitutes abearing sleeve part, opening along the one end portion, of the bearingstructural unit.
 8. A method of manufacturing a lubricant-impregnatedporous bearing component, in which a bearing retainer having a bearingretaining cavity at least one end of which is open, and a tubular porousbearing material retained in the bearing retaining cavity in the bearingretainer constitute a bearing structural unit in which thebearing-retaining-cavity interior except for the one end portion of thebearing retainer has airtightness against the outside, the methodimpregnating the porous bearing material with a lubricant, andcomprising: placing the bearing structural unit within areduced-pressure space; with the one end of the bearing retaining cavitydirected down, immersing in, or contacting on, the lubricant the one endportion of the bearing retainer to put the one end of the bearingretaining cavity in an occluded state; and thereafter, while maintainingthe one end of the bearing retaining cavity occluded by the lubricant,restoring the pressure to impregnate the porous bearing material withthe lubricant.
 9. A method of manufacturing a fluid dynamic-pressurebearing furnished with a shaft-end structural unit having a centrallyprotruding shaft, a shaft-end ringlike planar surface extending radiallyoutward from the outer circumferential surface of the base of the shaft,and a cylindrical surrounding wall surface standing out, in the samedirection as the shaft, from the shaft-end ringlike planar surface alongits outer periphery, and furnished with a bearing structural unit openalong one side, having a journaling bore into which the shaft isinserted, a closed-off endface axially opposing the leading-end surfaceof the shaft, an open-side endface axially opposing the shaft-endringlike planar surface, and a bearing-side outer circumferentialsurface confronting the cylindrical surrounding wall surface across adiametrical interspace; the bearing structural unit retaining, in abearing retaining cavity of a unilaterally open-ended bearing retainer,a sleeve-shaped porous bearing material forming the journaling bore, andthe porous bearing material being impregnated with lubricant; the fluiddynamic-pressure bearing being constituted such that a series of bearinggaps filled with lubricant is formed between the bearing structuralunit, and the shaft and the shaft-end ringlike planar surface, and suchthat the lubricant interposes continuously between the cylindricalsurrounding wall surface and the bearing-side outer circumferentialsurface; the fluid-dynamic-pressure bearing manufacturing methodcomprising: placing the bearing structural unit within areduced-pressure space; with the one end of the bearing structural unitdirected down, immersing the one end portion in, or contacting the oneend portion on, lubricant arranged within the reduced-pressure space toput the one end portion in state in which it is occluded by thelubricant; and thereafter, while maintaining the one end portionoccluded by the lubricant, restoring the pressure to impregnate theporous bearing material with the lubricant.